gmx-principal - Calculate principal axes of inertia for a group of atoms

       2025, GROMACS development team

2025.0                                            Feb 10, 2025                                  GMX-PRINCIPAL(1)

gmxprincipal calculates the three principal axes of inertia for a group of atoms. NOTE: Old versions of
       GROMACS wrote the output data in a strange transposed way. As of GROMACS 5.0, the output file  paxis1.dat
       contains  the  x/y/z components of the first (major) principal axis for each frame, and similarly for the
       middle and minor axes in paxis2.dat and paxis3.dat.

       gmx-principal - Calculate principal axes of inertia for a group of atoms

       Options to specify input files:

       -f[<.xtc/.trr/...>](traj.xtc)
              Trajectory: xtctrrcptgrog96pdbtng-s[<.tpr/.gro/...>](topol.tpr)
              Structure+mass(db): tprgrog96pdb brk ent

       -n[<.ndx>](index.ndx)(Optional)
              Index file

       Options to specify output files:

       -a1[<.xvg>](paxis1.xvg)
              xvgr/xmgr file

       -a2[<.xvg>](paxis2.xvg)
              xvgr/xmgr file

       -a3[<.xvg>](paxis3.xvg)
              xvgr/xmgr file

       -om[<.xvg>](moi.xvg)
              xvgr/xmgr file

       Other options:

       -b<time>(0)
              Time of first frame to read from trajectory (default unit ps)

       -e<time>(0)
              Time of last frame to read from trajectory (default unit ps)

       -dt<time>(0)
              Only use frame when t MOD dt = first time (default unit ps)

       -tu<enum>(ps)
              Unit for time values: fs, ps, ns, us, ms, s

       -[no]w(no)
              View output .xvg, .xpm, .eps and .pdb files

       -xvg<enum>(xmgrace)
              xvg plot formatting: xmgrace, xmgr, none

       -[no]foo(no)
              Dummy option to avoid empty array

gmx(1)

       More information about GROMACS is available at <http://www.gromacs.org/>.

          gmx principal [-f[<.xtc/.trr/...>]] [-s[<.tpr/.gro/...>]]
                       [-n[<.ndx>]] [-a1[<.xvg>]] [-a2[<.xvg>]]
                       [-a3[<.xvg>]] [-om[<.xvg>]] [-b<time>] [-e<time>]
                       [-dt<time>] [-tu<enum>] [-[no]w] [-xvg<enum>]
                       [-[no]foo]